Nonperforming Assets (Additional Information) (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Other Real Estate	[1]	$ 52	$ 57
Accrual Loans [Member]
Mortgage Loans in Process of Foreclosure, Amount		108	101
Proceeds due from FHA or VA [Member]
Mortgage Loans in Process of Foreclosure, Amount		100	97
Other Real Estate		49	45
Nonaccrual loans [Member]
Mortgage Loans in Process of Foreclosure, Amount		89	73
Residential Portfolio Segment [Member]
Other Real Estate		49	51
Commercial Portfolio Segment [Member]
Other Real Estate		2	4
Land and Land Improvements [Member]
Other Real Estate		$ 1	$ 2

[1] Does not include foreclosed real estate related to loans insured by the FHA or guaranteed by the VA. Proceeds due from the FHA and the VA are recorded as a receivable in Other assets in the Consolidated Balance Sheets until the property is conveyed and the funds are received. The receivable related to proceeds due from the FHA and the VA totaled $49 million and $45 million at September 30, 2018 and December 31, 2017, respectively.